Custom field require when copying task

Added by Sergei Cherevko 3 months ago

I create custom field "Spend time"
how to setup requiring this field only for people who close task?

When i create a task i do not want to require filling this field, because i creator this task and i do not must fill this field
When i copy task i do not want to require filling this field, because i creator this task and i do not must fill this field

In all another cases (such as close task) i want to require fill this field, in other cases - not.

How to adjust?

redmine 2.6.6